Process for producing nitric acid



. BAN IGAN.

PROCESS FOR PRODUCING N'lTRlC ACID.

APPLICATION FILED MAR. 12, I919.

Patnted Mar. 2, 1920.

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TTTIIIIKIII QWI W/ r/vEss T. F. BANIGAN. PROCESS FORPRODUCING NITRIC ACID. APPLLCATION FILED MAR. 12, 9 9- 1,332, 1 95. Patented Mar. 2, 1920.

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STATES PATENT OFFICE.

THOMAS E. BANIGAN, OF EVIL, NEW JERSEY, ASSIGNOR '10 HEBCULE POWDER COIPANY, OF WILMINGTON, DELAWARE, A CORPORATION OF DELAWARE.

PROCESS FOR PRODUCING NITRIC ACID.

Specification of Letters Patent.

Patented Mar. 2, 1920.

Original application filed August 22, 1918, Serial 110. 250,978. Divided and this application filed Iarch 18, 1919. Serial H0. 282,205.

' a full, clear, and exact description, reference being had to the accompanying drawings,

which form a part of this specification.-

While a careful study of the art convinced me that known processes for producing nitric acid by interaction of sodium nitrate and niter cake were fundamentally sound, still it is a fact that none of them yields, on a commercial scale, nitric acid in any deree approaching a quantitative yield. among the defects'of known processes may be recited the following: thermal inefliciency; failure to eliminate residual sodium sulfate from the retort; excessive decomposition and only partial elimination of nitric acid and a yield of nitric acid which is far from quantitative and is seriously lacking in purity and uniformity;- low capacity per unit of time; and prohibitive labor cost and unkeep charges .on the equipment.

I have discovered that all the foregoing defects of the known processes may be remedied by the following means, namely: differential heating of the retort so as to provide a relatively high temperature zone adjacent the end for the discharge of solid or fused material; rest-rainin the tendency of the material to sinter an cling to the walls of the retort; scraping from the walls of the retort any adhering sodium sulfate, breaking up lumps and preventing the consolidation of material as it fuses; and ap plying a degree of suction to the retort while restraining free admission of air at the discharge end.

While the execution of the process is not dependent upon the use of any particular apparatus, I prefer to employ the apparatus shown in the accompanying drawings, which has been constructed on a 'full sized scale, practically operated and tested and demonstrated to be adapted to successfully carry out the process and produce so large a yield of nitri acid as to be commercially practicable.

- In the drawings Figure 1 is a, sectional view of the furnace for driving off the nitric acid from the mixture. a

Fig. 2 is a section through the retort of F ilg. 1.

ig. 3 is an elevation of the condensation and absorption apparatus.

The retort comprises a long rotatable iron 0 linde'ra inclined about one-half inch to t e foot and turning at opposite ends in machined, air-tight bearings b and c. The lower bearing a is of hollow T-shape, and affords a passage from the retort a to the bin (5. Hollow bearing 0 is provided with an air admission pipe controlled by a valve 2.

The retort is inclosed in a long, narrow brick furnace e. The end of the furnace adjoin'uzig the lower end of the retort is provide with a fire-box f. Between the fire-box and the other end of the furnace is a bed of cinders g. The products of combustion pass up around and thence along the retort and escape by the stack h. Outside the end of the furnace adjacent the higher end of the retort is erected a frame 2' carrying driving mechanism 7' by which the driving power is transmitted from a motor to a sprocket wheel k secured to the higher end of the retort. The retort at opposite ends rests on rollers n, 0, turning 1n bearings on the frame i and on the fram for the bin (Z.

Extending through the end closure 6 is a feed tube p containing a power driven feed screw r and communicating with a hoppers.

Also extending through the end closure b is a t connected to apipe 1; which commumcates, by a swiveled connection, with the admission pipe of a. condensing and absorption system. an represents the condenser and y the absorption apparatus. These per se are of standard construction and therefore need not be described in detail.

The charge, which is placed in the hopper and fed continuously into the retort, consists of a mixture of pulverized niter cake and sodi m nitrate, preferably ground nitric acid occurs.

separately, to which is also preferably added ground sodium sulfate or other material to prevent the mixture from sintering and to give a friable residue which will not cling to the retort. The construction and arrangement of the furnace and retort are such that the retort is heated unequally, the zone of highest heat being at the lower end of the retort, the temperature gradually d1- minishing toward the higher end of the retort. Hence the charge is subjected to a gradually increasing temperature as it moves progressively through the retort. The charg- 1ng end of the retort is therefore relatively cool. The arrangement permits of a gradual evolution of nitric acid at such a low temperature that minimum decomposition of As the charge approaches the lower or discharge end, it reaches the zone of maximum temperature, wherein complete elimination of nitric acid is effected. Thus, when a temperature promotive of decomposition is reached, thenitric acid has been already largely eliminated; and, further, the charge is within the zone of highest temperature during only a relatively short interval of time, The results are: (1) maximum heat efficiency; (2) maximum production of nitric acid; (3) minimum decomposition of nitric acid; (4) production of high grade sodium sulfate.

So far as described, the mechanical difiiculties of carrying out the process are only partly overcome, because, as the mixture is fed into the retort, it melts into a viscous mass which hardens as the nitric acid is driven off, forming normal sodium sulfate with a high melting point, the fused mixture having an extreme tendency to harden to the walls of the retort. Mere agitationand stirring or hammering on the outside walls of the retort do not sufiice to prevent this adhesion. I have found, however, that if, during the process, the walls of the retort are scraped free from adhering sodium sulfate and the lumps broken up, nitric acid will be thoroughly eliminated and the residual sodium sulfate pulverized. To effect this operation I prefer to use a steel rail shown at w), a double T-iron, or any other sharp-edged, heavy iron bar, which is laid loosely inside and lengthwise of the retort so as to be free to tumble about as the retort revolves. I

The nitric acid, as produced in the retort, escapes by Way of tube 15 and pipe 'v to t(he cpndensation and absorption apparatus m, 3 v a It is preferred to connect the last absorp tion tower of the series with a pipe in which a slight vacuum is maintained, which is ef fective throughout the entire apparatus and causes a slow flow of air through the retort to oxidize the lower oxidsof nitrogen and discharge end assist in sweeping the nitric acid out of the retort. For this reason the closure at the of theretort should be airtight, or nearly so, as hereinbefore described.

ree admission of air at the discharge end of the retort should be avoided.

I do not herein claim the apparatus shown and described for carrying out my process, as the same forms the subject-matter of a separate application filed August 22, 1918, Serial N 0. 250,978, of which this application is a division.

Having now fully described my invention, what I claim and desire to protect by Let ters Patent is:

1. The process of producing nitric acid and sodium sulfate from a mixture of pulverized niter cake and sodium nitrate which comprises'imparting to a stream of the mixture a combined tumbling and steadily progressive movement and replenishing the stream at one end and discharging it at the other end, differentially heating the stream by creating a zone of relatively high temperat-uretoward the discharge end and a zone of relatively low temperature toward the supply end, and causing the nitric acid evolved to flow in a direction opposite to the travel of the stream.

2. The process of producing nitric acid and sodium sulfate from a mixture of pul" verized niter cake and sodium nitrate which comprises imparting to the stream of the mixture a combined tumbling and steadily progressive movement and subjecting the mixture as it advances to a gradually increasing temperature.

3. The process of producing nitric acid and sodium sulfate from a mixture of pulverized niter cake and sodium nitrate which comprises imparting to the stream of the mixture a progressive movement, differentially heating thestream by creating a zone of maximum temperature toward the discharge end of the stream, and during the application of heat preventing the consolida tion of material as it fuses, breaking up the lumps, and pulverizing the sodium sulfatg resulting from the elimination of nitric aci 1. The process of producing nitric acid and sodium sulfate from a mixture of pulverized niter cake and sodium nitrate which comprises imparting to a stream of the mixture a combined tumbling and steadily pro' gressive movement. replenishing the stream at one end and discharging it at the other end, and during said operation scraping the fused material from the inner wall of the retort. 5. The process of producing nitric acid and sodium sulfate from a mixture of pulverized niter cake and sodium nitrate which comprises imparting to an inclosed stream of the mixture :1 combined tumbling and steadily progressive movement and continually replenishing the stream at one end and discharging it at the other end, diflerentially heating the stream by creating a zone of'relatively high temperature toward the discharge end and a zone of relatively low temperature 7 toward the supply end, creating a suction to cause a slow flow of 10 airin a, direction opposite to the flow of the solids, thereby oxidizing the lower oxids of nitrogen and assisting the flow of nitric acid in the direction of suction, and restraining the free admission of air to the discharge end of the stream of solids.

In testimony of which invention, I have hereunto set my hand, at Kenvil, N. J on this 7th day of March, 1919.

THOMAS F. BAXIG'AN. 

